
D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 609 
over this district of the Highlands, detritus formerly existed to such an extent, 
that blockages might have been formed by it, to keep up lakes existing in the 






































Fig. 7. (See p. 608.) 
Section showing lake supposed to have formerly existed near Monessie. 
country to the requisite height ; and (2.) That there are many cases now in the 
Highlands, of lakes kept up in this manner ; (3.) That lakes have subsided, and 
even drained altogether, by the wearing down and removal of detrital blockages 
through the action of rivers. 
~ 
mw A 
SS, 

Fig. 8. (See p. 608.): 
Section showing the same spot near Monessie after the lake was drained, by the 
River Spean having cut through the detritus and subjacent rocks. 
5. If these views be applied to the Parallel Roads in the respective glens, 
they will be found sufficient to,explain by what means these Roads stopped 
at the places marked on the map. 
(1.) As the two shelves of Glen Gluoy appear only in the upper part of the 
glen, some blockage must have existed at its mouth. I shall revert to this Glen 
Gluoy blockage in a subsequent part of the paper when discussing the blockage 
of the Great Glen. Meanwhile, I would refer to a peculiarity in Glen Gluoy, that 
the upper shelf extends farther down the glen than the lower shelf. A B in 
fig. 9 is the hill forming one side of the valley on which the shelves are 
marked, C C is the highest shelf, and D D the lowest. The greater extension of 
the upper shelf may be accounted for, by supposing that the detrital blockage E, 
sloped in the way shown in the figure, which is the usual form of a lake bottom. 
(2.) It is not difficult to understand how or why the blockage changed posi- 
tion and level, if it was detritus. There are, in all the Glens, multitudes of 
